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Purifying qubits in NMR quantum information processing

Colm Ryan
Institute for Quantum Computing (IQC)
June 02, 2007

PIRSA:07060015
Quantum Information
Degradation of a quantum directional reference frame

Lana Sheridan
Mission College
June 02, 2007

PIRSA:07060014
Quantum Information
Quantum Key Distribution Networks

Douglas Stebila
Institute for Quantum Computing (IQC)
June 02, 2007

PIRSA:07060013
Quantum Information
Towards the Production of Entangled Photon Pairs in Optical Fiber via Four-Wave Mixing

Joshua Slater
University of Calgary
June 02, 2007

PIRSA:07060012
Quantum Information
Distributed phase reference schemes for QKD: Explicit attacks and security considerations

Cyril Branciard
Université de Genève
June 02, 2007

PIRSA:07060011
Quantum Information
An Introduction to Decoherence-Free Subspaces

Martin Laforest
Institute for Quantum Computing (IQC)
June 02, 2007

PIRSA:07060003
Quantum Information
Information Flow in the Heisenberg Picture

Cédric Bény
Leibniz University Hannover
June 02, 2007

PIRSA:07060009
Quantum Information
Quantum Mechanics in Phase Space
June 02, 2007

PIRSA:07060008
Quantum Information
An Introduction to One-Way Patterns
June 01, 2007

PIRSA:07060007
Quantum Information
Cluster State Quatum Computing in Optical Fibres

Yasaman Soudagar
Polytechnique Montreal
June 01, 2007

PIRSA:07060006
Quantum Information
A New Protocol for Loss-Tolerant Quantum Coin Tossing
June 01, 2007

PIRSA:07060005
Quantum Information
Degradability of Bosonic Gaussian Channels

Filippo Caruso
Scuola Normale Superiore di Pisa
June 01, 2007

PIRSA:07060004
Quantum Information

Purifying qubits in NMR quantum information processing

Colm Ryan
Institute for Quantum Computing (IQC)
June 02, 2007

PIRSA:07060015
Quantum Information
Any implementation of a quantum computer will require the ability to reset qubits to a pure input state, both to start the computation and more importantly to implement fault-tolerant operations. Even if we cannot reset to a perfectly pure state, heat-bath algorithmic cooling provides a method of purifying mixed states. By combining the ability to pump entropy out of the system through a controllable interaction with a heat bath and coherent control of the qubits, we are able to cool a subset of the qubits far below the heat bath temperature. Here we show an implementation of this cooling in a solid state NMR quantum information processor which offers high fidelity control of the qubit system and controllable access to a heat bath. We demonstrate an implementation of multiple rounds of heat-bath algorithmic cooling on three qubits and discuss the improvements in control techniques which have allowed us to show the purification of a single qubit to one and a half times the heat bath polarization.
Degradation of a quantum directional reference frame

Lana Sheridan
Mission College
June 02, 2007

PIRSA:07060014
Quantum Information
In this study, we are interested in the practical question of how many times a quantum directional reference frame (i.e., a spin-J system) can be used to perform a certain task with a given probability of success, under the assumption that the quantum directional reference frame evolves under a map that is covariant under rotations in SU(2). Our main theorem restricts the form of the state of the quantum reference frame as a function of how many times the covariant map was applied to it. Our results are a generalization of the paper of Bartlett el al. on the degradation of reference frames, and can be used to analyze certain types of interactions on a spin-J system.
Quantum Key Distribution Networks

Douglas Stebila
Institute for Quantum Computing (IQC)
June 02, 2007

PIRSA:07060013
Quantum Information
Current physical implementations of quantum key distribution (QKD) require communicating parties to be close together. We will explore methods for allowing parties separated by long distances to communicate by combining many QKD links in a network and discuss the resulting security properties.
Towards the Production of Entangled Photon Pairs in Optical Fiber via Four-Wave Mixing

Joshua Slater
University of Calgary
June 02, 2007

PIRSA:07060012
Quantum Information
Previous experiments on the production of entangled photon pairs directly in optical fiber via four-wave mixing (FWM) have used a single pump laser and produced signal and idler photons with similar wavelengths. We will present the first results of our investigation into the production of widely separated entangled photon pairs via FWM in optical fiber using multiple pump lasers also at widely separated wavelengths. This source will have important applications in quantum cryptography and computation. As fiber optic and free space quantum communication networks require photons at different wavelengths (1550 nm and around 800 respectively) this source will make hybrid quantum cryptography networks achievable and could also be used as a heralded optical fiber source of single photons.
Distributed phase reference schemes for QKD: Explicit attacks and security considerations

Cyril Branciard
Université de Genève
June 02, 2007

PIRSA:07060011
Quantum Information
"Distributed phase reference schemes are a new class of protocols for Quantum Key Distribution, in which the quantum signals have overall phase-relationships to each other. This is expected to protect against some loss-related attacks. However, proving the full security of these schemes is a new challenge for theorists, as one can no longer identify individual signals (such as qubits in BB84, for instance), and so the security proof techniques do not apply directly.In this talk I will present two such protocols (the Differential Phase Shift and the Coherent One Way protocols). Their ""unconditionnal security"" has not been proven yet, but I will present some specific attacks on these schemes, which give us upper bounds for the security, as well as a ""feeling"" on how these schemes should perform."
An Introduction to Decoherence-Free Subspaces

Martin Laforest
Institute for Quantum Computing (IQC)
June 02, 2007

PIRSA:07060003
Quantum Information
Information Flow in the Heisenberg Picture

Cédric Bény
Leibniz University Hannover
June 02, 2007

PIRSA:07060009
Quantum Information
Quantum Mechanics in Phase Space
June 02, 2007

PIRSA:07060008
Quantum Information
Many authors have proposed what are known as "phase-space" or "classical" representations of quantum mechanics. A unifying framework is given which illustrates the relationship among these various theories. Examples relevant to quantum computing will be given.
An Introduction to One-Way Patterns
June 01, 2007

PIRSA:07060007
Quantum Information
The one-way measurement model is a model of quantum computation which is intriguing for its' potential as a means of implementing quantum computers, but also for theoretical purposes for the different way in which it allows quantum operations to be described. Instead of a sequence of unitary gates on an array of ``wires'', operations are described in terms of emph{patterns}, consisting of a graph of entanglement relations on a set of qubits, together with a collection of measurement angles for these qubits (except possibly for a subset which will support a final quantum state). In this introductory talk, I describe the relationship between patterns in the one-way measurement model to quantum circuits, and explore patterns which represent unitary operations but which emph{don't} have direct analogues in the circuit model.
Cluster State Quatum Computing in Optical Fibres

Yasaman Soudagar
Polytechnique Montreal
June 01, 2007

PIRSA:07060006
Quantum Information
In this presentation I will briefly explain the cluster state model of quantum computing. Then will talk about a scheme that uses polarization and time-bin degrees of freedom of photons in optical fibres for the optical realization of this model. We are currently working on the implementation of this scheme in our lab.
A New Protocol for Loss-Tolerant Quantum Coin Tossing
June 01, 2007

PIRSA:07060005
Quantum Information
Quantum coin tossing is a cryptographic task in which two parties, Alice and Bob, wish to generate a shared random bit but do not necessarily trust each other. This task is completely impossible to realize with classical asynchronous communication but becomes at least partially feasible when quantum communication is also available. The best quantum protocol known so far, due to Ambainis, uses qutrits and is near optimal in the sense that either party can bias the outcome with at most a 75% probability of success. However, when the transmission of the link is below 50%, Ambainis' protocol can be easily broken by a cheating Bob. This problem arises whenever there exists a conclusive measurement allowing Bob to obtain with certainty, although with a probability less than one, relevant information about the state sent by Alice. In this talk, we will present a new protocol for quantum coin tossing that does not suffer from this weakness and, as a consequence, is loss-tolerant. We discuss possible attacks and argue that the protocol is secure. Technologically, the implementation of this protocol is no more difficult than implementing entangled quantum key distribution with qubits. This is joint work with Guido Berlin, Gilles Brassard and Nicolas Godbout.
Degradability of Bosonic Gaussian Channels

Filippo Caruso
Scuola Normale Superiore di Pisa
June 01, 2007

PIRSA:07060004
Quantum Information
The notion of weak-degradability of quantum channels is introduced by generalizing the degradability definition given by Devetak and Shor. Exploiting the unitary equivalence with beam-splitter/amplifier channels we then prove that a large class of one-mode Bosonic Gaussian channels are either weakly degradable or anti-degradable. In the latter case this implies that their quantum capacity Q is null. In the former case instead, this allows us to establish the additivity of the coherent information for those maps which admit unitary representation with single-mode pure environment.

Title	Date	Collection	Type	Info
Purifying qubits in NMR quantum information processing	2007‑06‑02	The Fourth Annual Canadian Quantum Information Students' Conference - 2007	Conference	View details
Degradation of a quantum directional reference frame	2007‑06‑02	The Fourth Annual Canadian Quantum Information Students' Conference - 2007	Conference	View details
Quantum Key Distribution Networks	2007‑06‑02	The Fourth Annual Canadian Quantum Information Students' Conference - 2007	Conference	View details
Towards the Production of Entangled Photon Pairs in Optical Fiber via Four-Wave Mixing	2007‑06‑02	The Fourth Annual Canadian Quantum Information Students' Conference - 2007	Conference	View details
Distributed phase reference schemes for QKD: Explicit attacks and security considerations	2007‑06‑02	The Fourth Annual Canadian Quantum Information Students' Conference - 2007	Conference	View details
An Introduction to Decoherence-Free Subspaces	2007‑06‑02	The Fourth Annual Canadian Quantum Information Students' Conference - 2007	Conference	View details
Information Flow in the Heisenberg Picture	2007‑06‑02	The Fourth Annual Canadian Quantum Information Students' Conference - 2007	Conference	View details
Quantum Mechanics in Phase Space	2007‑06‑02	The Fourth Annual Canadian Quantum Information Students' Conference - 2007	Conference	View details
An Introduction to One-Way Patterns	2007‑06‑01	The Fourth Annual Canadian Quantum Information Students' Conference - 2007	Conference	View details
Cluster State Quatum Computing in Optical Fibres	2007‑06‑01	The Fourth Annual Canadian Quantum Information Students' Conference - 2007	Conference	View details
A New Protocol for Loss-Tolerant Quantum Coin Tossing	2007‑06‑01	The Fourth Annual Canadian Quantum Information Students' Conference - 2007	Conference	View details
Degradability of Bosonic Gaussian Channels	2007‑06‑01	The Fourth Annual Canadian Quantum Information Students' Conference - 2007	Conference	View details

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